; Program SSC_DEMO.SRC (Mini SSC educational demo). ; Written in Parallax dialect of PIC assembly language. ; This program is a demo version of the firmware for the Mini SSC, ; a device that controls eight radio-control servos in accordance with ; instructions recieved over a 2400- or 9600-baud serial hook-up. The ; commercial Mini SSC also recognizes individual board IDs, allowing up ; to 32 controller (256 servos!) on one serial port. This demo version ; is not addressable, works at a fixed rate of 2400 baud, and controls ; just on e servo. However, it has the same basic structure as the full-up ; program. It is provided for novice PIC users interested in a method for ; Running two time-sensitive processes concurrently. ; Serial data is accepted through ra.3; servo pulses (1 to 2 ms, repeated ; approx. 60 Hz) are output at rb.0. This program runs propertly on a ; PIC16C61, 71, or 84 with an 8 MHz clock. At the time this program was ; written, the 16C61 was new, and PASMX/PEPX did not recognize it as a ; valid device. Fortunately, the '61 programs just find from code generated ; for a 71 or 84 (provided you don't use the special features of those ; devices). If you program a 61, be sure that PEPX is set for a 71 - setting ; it for an 84 will cause programming errors. device pic16c71, xt_osc, wdt_off, protect_off, pwrt_off id 'SVDM' ;Symbols (constants) used in the program. one_ms = 6 ; value to load into RTCC for 1-ms delay ser_pin = ra.3 ; Serial-input pin stb24 = 44 ; Start delay for 2400 bps @ 8 Mhz bit24 = 164 ; Full delay for 2400 bps @ 8 Mhz ; Variable declarations. Variables for this program begin at address ; 0C hex, placing them above the PIC's special-function registers. org 0Ch svo_PC ds 1 ; Program segment counter for servo ISR w_copy ds 1 ; Copy of w register made by ISRdelay_cnt ds 1 ; Counter for serial delay routines. bit_cnt ds 1 ; Number of received bits. rcv_byte ds 1 ; The received byte temp ds 1 ; Reusable temporary storeage position ds 1 ; Position value. end_frame ds 1 ; Counter for end of frame delay ; Upon reset the PIC first executes the code located at address 0. In this ; demo, it jumps to the beginning of the foreground program located at ; "start" When an interrupt occurs, the PIC jumps to address 4. This is ; where the interrupt handler is located. org 0 jmp start ; The reset vector. org 4 ; The interrupt handler. ; The interrupt-service routine (ISR). When RTCC overflows, the resulting ; interrupt sends the program here. This ISR stores the w and status ; registers, then jumps to the program segment stored in svo_PC. ; The segments load RTCC and start and stop the servo pulses ; based on the data found in the variable position. Once finished, they ; store the address of the next segment to be executed, restore the ; registers, and execute the reti (return from interrupt) instruction. do_servos clrb rtif ; Reset timer-interrupt flag. mov w_copy,w ; Save the status and W registers. mov w,<>status ; Swap status into w. mov st_copy,w mov w,svo_PC ; Move servo program couter to w. jmp w ; Jump to segment pointed to by svo_PC ; Segment zero starts the servo pulse by weiring a high to rb.0 and ; setting RTCC to interrupt again after a 1-ms delay, it loads segment 1 ; into tho "servo program counter" that do_servos used to jump to the ; correct segment of the routine. seg_0 setb rb.0 ; Initiate pulse mov rtcc,#one_ms ; Set up 1-ms delay. mov svo_PC#seg_1 ; Execute next segment at 1-ms timeout mov w,<>st_copy ; Restore the status register and W. mov status, w swap w_copy mov w,<>w_copy ; Return from interrupt. reti seg_1 mov w,/position ; Load the inverse of the position value mov rtcc,w ; into the rtcc to create delay mov svo_PC,#seg_2 ; Execute next segment after timeout mov w,<>st_copy ; Restore the status register and W. mov status,w swap w_copy mov w,<>w_copy reti ; Return from interrupt seg_2 clrb rb.0 ; End the pulse. mov w.position ; Load the non-inverted position value mov rtcc.w ; into rbcc to create a pad delay mov svo_PC,#seg_3 ; Execute next segment after time out. mov end_frame,#14 ; Wait 14 ms before seg_0 (see seg_3) mov w,<>st_copy ; Restore the status register and W. mov status,w swap w_copy mov w,<>w_copy reti ; Return from interrupt seg_3 mov rtcc,#one_ms ; Set up a 1-ms delay djnz end_frame,:cont ; Repeat this segment untill end_frame=0 mov svo_PC,#seg_0 ; When end_frame runs out, point to seg_0 :cont mov w,<>st_copy ; Restore status register and W. mov status,w swap w_copy mov w,<>w_copy reti ; Return from interrupt ; Start marks the beginning of the initialization code that sets up the ; program. It configures the RTCC to increment off the system clock ; through a divide-by-8 prescaler. At 8 MHz, that makes one RTCC tick ; equal to 4 microseconds - the desired resolution of our servo-pulse ; generator. Start also sets the servo routine's program counter to ; segment 0. start mov svo_PC,#seg_0 ; Point to base segment of ISR setb rp0 ; Switch to register page 1. clr wdt ; Transfer the prescaler to RTCC. mov option,#10000010b ; and set it for /8 clrb rp0 ; Back to page 0. mov intcon,#10100000b ; Turn on RTCC interrupt. main mov lra,#1000b ; Serial input is ra.3. mov lrb,#0 ; make rb all outputs. :start_bit ; Receive serial data. snb ser_pin ; Look for start bit. jmp :start_bit ; No start bit? keep watching. call serl_in ; Get the serial data. mov delay_cnt,#bit24 ; Stop-bit delay. call delay ; Wait for stop bit. mov posiiton,rcv_byte ; Move data to position goto main ; Endless loop. ; Subroutine to read in serial data from the port bit ser_pin. ; Note that there's no stop-bit delay. Callers may incorporate ; this delay into other operation. serl_in mov bit_cnt,#8 ; Eight data bits. clr rcv_byte ; Get ready for new data. mov delay_cnt,#stb24 ; Start-bit delay call delay ; Wait untill first data bit. :rcv mov delay_cnt,#bit24 ; Full-bit delay. call delay ; Wait for bit. movb c,ser_pin ; Put data bit into carry. rr rcv_byte ; Rotate bit into byte. djnz bit_cnt,:rcv ; Not full? Get next bit. ret ; Simple do-nothing loop for variable length dealys. Program must ; logad delay_cnt before calling this routine. delay jmp $+1 djnz delay_cnt,delay ret
|file: /Techref/microchip/sscdemo.htm, 6KB, , updated: 1999/2/16 23:51, local time: 2020/7/11 01:14,
|©2020 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.sxlist.com/TECHREF/microchip/sscdemo.htm"> microchip sscdemo</A>
|Did you find what you needed?|
Welcome to sxlist.com!
& kind contributors
just like you!
Please don't rip/copy
Copies of the site on CD
are available at minimal cost.
Welcome to www.sxlist.com!